1 files changed, 22 insertions, 3 deletions

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 6d1cbdfc9b2a..b64502dfa9f4 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -296,8 +296,13 @@ static int iommu_init_device(struct device *dev)
         } else
                 dma_pdev = pci_dev_get(pdev);
 
+        /* Account for quirked devices */
         swap_pci_ref(&dma_pdev, pci_get_dma_source(dma_pdev));
 
+        /*
+         * If it's a multifunction device that does not support our
+         * required ACS flags, add to the same group as function 0.
+         */
         if (dma_pdev->multifunction &&
             !pci_acs_enabled(dma_pdev, REQ_ACS_FLAGS))
                 swap_pci_ref(&dma_pdev,
@@ -305,14 +310,28 @@ static int iommu_init_device(struct device *dev)
                                           PCI_DEVFN(PCI_SLOT(dma_pdev->devfn),
                                           0)));
 
+        /*
+         * Devices on the root bus go through the iommu.  If that's not us,
+         * find the next upstream device and test ACS up to the root bus.
+         * Finding the next device may require skipping virtual buses.
+         */
         while (!pci_is_root_bus(dma_pdev->bus)) {
-                if (pci_acs_path_enabled(dma_pdev->bus->self,
-                                         NULL, REQ_ACS_FLAGS))
+                struct pci_bus *bus = dma_pdev->bus;
+
+                while (!bus->self) {
+                        if (!pci_is_root_bus(bus))
+                                bus = bus->parent;
+                        else
+                                goto root_bus;
+                }
+
+                if (pci_acs_path_enabled(bus->self, NULL, REQ_ACS_FLAGS))
                         break;
 
-                swap_pci_ref(&dma_pdev, pci_dev_get(dma_pdev->bus->self));
+                swap_pci_ref(&dma_pdev, pci_dev_get(bus->self));
         }
 
+root_bus:
         group = iommu_group_get(&dma_pdev->dev);
         pci_dev_put(dma_pdev);
         if (!group) {